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  1. #31
    Nicholas Lindan's Avatar
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    Quote Originally Posted by Denis P. View Post
    Thanks for the help, Nicholas.

    The connector block is fed by 24V current from the transformer, and has two 24V 200W halogen bulbs attached to it. I managed to decypher the following:

    CGS
    010
    1 (ohm - I don't know how to insert the "Omega" symbol )
    5%
    72 47
    1 ohm +/-5%, 10 watts, made on the 47th week of 1972 [at a guess, looks like a date code]

    That shouldn't be that hard a part to find. You can use any wattage rating as long as it is above 10 watts. And it doesn't have to be made on the 47th week.

    How are these wired? Is it in series with the lamps? if so something is funny, 200W/24V lamps draw ~8 amps and 16 amps (two lamps) flowing through a .3 watt resistor (the effect of 3 resistors in parallel) is about 80 watts. Unless the fan is blowing on them full blast those babies should smoke.

    Is it possible they are wired to the fan circuit? Though that doesn't make any sense either.

    If they are wired with the lamps their purpose is to extend lamp life by limitting the inrush current into the cold lamps and to drop the voltage to the lamps by about 5 volts: so if they are on a transformer rated at 28V the voltage to the lamps would be 23 volts - about right.
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    f-Stop Timers - Enlarging Meters
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  2. #32
    Denis P.'s Avatar
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    Quote Originally Posted by Marco Gilardetti View Post
    Hello Denis. Either one of the following:

    1) Load.

    2) Tolerance.
    Thanks for the explanation, Marco - I guess you're right. I forgot that there's no load

    Quote Originally Posted by Nicholas Lindan View Post
    1 ohm +/-5%, 10 watts, made on the 47th week of 1972 [at a guess, looks like a date code]
    ...
    If they are wired with the lamps their purpose is to extend lamp life by limitting the inrush current into the cold lamps and to drop the voltage to the lamps by about 5 volts: so if they are on a transformer rated at 28V the voltage to the lamps would be 23 volts - about right.

    Nicholas, they are wired in parallel - see the photo attachment a few posts above.
    They are wired with the lamps - your explanation, together with Marco's explains my results in measuring incoming voltage at about 28V - together with the load and resistors, the voltage should drop to the one more acceptable for the lamps which are rated 24V/200W.
    Your explanation is in line with another I got from a friend today - he's a ham radio operator, with a long experience in home electronics, amps, transmitters, etc. - he said the same thing - those resistors probably limit the inrush current....

    And yes, there's a fan attached

    But, the resistors seem to be OK. Measured together (at the connectors), they yield something like 0.8 ohms... I was just trying to understand what kind of replacement I would need - just in case these three turn out to be too unreliable.

    Looks like I'm beginning to understand the mechanics (and electronics) of this beast

    Thanks, guys - you're extremely helpful!

    Denis

  3. #33
    Nicholas Lindan's Avatar
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    Quote Originally Posted by Denis P. View Post
    Measured together (at the connectors), they yield something like 0.8 ohms
    It should be 0.33 ohms. Measure the resistance with both ohmeter probes on the same terminal and subtract this reading from the one across the resistor terminals. The ohmeter probes have their own resistance which must be subtracted.

    If it is really 0.8 ohms then one or two of the resistors have already fried and the remaining ones are about to. The lamps are going to be very unhappy. The resistor will be unhappy. Altogether, an unhappy situation.

    I suggest replacing them: from looks alone they are kaput, even if they in the end do measure 0.3 ohms they have been overstressed and show signs of overheating. If they had never overheated then all three of them would be shiney green vitreous enamel with clear markings and there would be no burn marks on the wiring. They are made to dissapate 10 watts each in free air and instead there are three of them crowded together each one dissapating 30 watts. This sort of problem is not uncommon in photographic equipment - it is the sort of thing my client firms do all the time, I get called in to find out why their products keep catching fire.

    From my calculations I would replace them with three 1.0 ohm 50 watt power resistors wired in parallel, as they are now. Your ham radio friend should be able to locate them for you.

    Mount the resistors so they are at least 1cm (1/4") apart. You may have to drill holes to mount the resistors.

    OTOH, the resistors as they are now may work fine till the end of time.

    If it were my enlarger I would replace them. YMMV. All advice worth price charged.
    DARKROOM AUTOMATION
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  4. #34
    Denis P.'s Avatar
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    Quote Originally Posted by Nicholas Lindan View Post
    ....
    Mount the resistors so they are at least 1cm (1/4") apart. You may have to drill holes to mount the resistors.

    OTOH, the resistors as they are now may work fine till the end of time.
    Thanks for the advice, I'll try to get new ones...

  5. #35
    Denis P.'s Avatar
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    The beast works!

    Yesterday I got new ceramic holders for the bulbs, installed them, and today I finally put the whole thing together. I set the head on the enlarger, took a deep breath, and pressed the button....

    Lo and behold, the thing works! Yipeee!

    I decided to leave the old resistors - getting replacement ones would take too long. Decided to try it out as is, with new lamps and holders. I have two sets of replacement lamps (4 spares), and I hope they won't be blowing out too frequently

    Now I only have to set up the working space (I'll have to make a table/stand for the L1000), and try to make some kind of DIY negative holder - the one I have is for 9x12, and it masks/crops too much of the 4x5 negatives. I'll try some mat board for a quick solution, and later try to make something more "permanent".

    In short, I'll be printing 4x5 negs soon!

    Thanks again for all the advice and help!

    Regards,

    Denis

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